Dryer control and dryer



June 29, 1965 w. w. PITTENDREIGH 3,191,917

DRYER CONTROL AND DRYER v Filed March so, 1962 2 Sheets-Sheet 1 INVENTOR. William WFazferzd@/i June 29, 1965 w. w. PITTENDREIGH DRYER CONTROL AND DRYER Filed March 30, 1962 2 Sheets-Sheet 2 INPUT I .2 flfifiusr mm.

R V m g 2200M r5141? 3 7/M F? j J mPur I j fx/musr 7:44;. i L- g Poo/v 75MB TlME m- S E007: 544/? it United States Patent 3,191,917 DRYER CONTROL AND DRYER William W. Pittendreigh, New Bedford, Mass., assignor, by mesne assignments, to McGraw-Edison Company Inc., Elgin, Ill., a corporation of Delaware Filed Mar. 30, 1962, Ser. No. 183,928

11 Claims. (Cl. 263-) This invention relates to dryers and more especially to commercial dryers of relatively large capacity which are used in launderettes and are required to be suitable for drying textile articles of mixed weight, composition and kind.

It is customary to install such apparatus for coin operation and for a given deposit the machine will run through a drying cycle of predetermined length, the drying period being calculated to etfectdrying of the heaviest articles expected to be processed. As a result, the lighter articles which hold little moisture are subjected to drying to: much too long a time at temperatures which are much too high and as a consequence the articles have a'harsh feel and their useful life is materially shortened. Closer control of the dryer cycle has been attempted by providing a moisture sensing device in the dryer chamber operable, when the moisture content reached a predetermined minimum, to cut-off the heat prior to the end of the cycle; however, such control is not wholly satisfactory, first, because the articles, when removed, are cold and have a damp feeling and, second, because the customer feels that she is being deprived of the full value for which she has paid by the premature ending of the heating cycle. 01? and on heating is employed in many drying systems to obtain drying without damage, that is, by supplying high temperature air for a predetermined length of time followed by low temperature air. However, as the articles ap proach dryness, the control of the duration of the off and on periods becomes too critical and it is, as a practical matter, impossible to avoid scorching the articles, particularly when the load is made up of fabrics of different degrees of heat resistance. Lower drying temperature could, of course, be used which would not be destructive to the most delicate of articles; however, the increased drying time makes such equipment uneconomical.

The principal objects of the invention are accordingly to eifect drying at as high a temperature as possible, during the initial wet or saturated stage of drying, to remove the water as rapidly as possible and hence to keep the drying cycle as short as possible and, during this time, to modulate the heat supplied in proportion to the in crease in dryness so as to avoid damage to the articles and/or inefficient use of heat, and when the moisture content has reached a preedtermined low level, reducing the heat input to a level for completing the cycle at a temperature which will not eifect bone dryness or be damaging to the articles and yet will deliver them at the end of the cycle, warm, fluffy and retaining their normal moisture content.

The foregoing objects are obtained herein by providing in combination with a drying chamber and means for establishing a flow of air through the chamber including an inlet through which air may enter the chamber and an outlet through which air is exhausted; variable capacity means for supplying heat to the chamber; means operable to change the capacity of said variable capacity means from a predetermined level at which rapid drying is effected to a predetermined lower level at which slow drying is eifected; means for modulating said variable capacity means at each level of its operation; and means operable to effect operation of the means for changing the capacity of the variable operable means when the residual moisture content of the material reaches a predetermined minimum. The means for supplying heat is a gas burner 3.1mm? Patented June 29, 1955 having a multi-position valve for supplying gas to the burner in different amounts. A sensing device, situated in the path of the input, effects positioning of the multiposition valve according to the moisture content of the material being dried. A second sensing device, situated in the exhaust stream, effects modulation of the valve at each of its two positions in proportion to the removal of moisture.

The invention will now be described in greater detail with reference to the accompanying drawings wherein:

FIG. 1 is a perspective view of a dryer, broken away in part, adjacent to the entry of hot air to the drying cham her and exit of moist air from the drying chamber;

FIG. 2 is a section through the gas metering valve showing the exhaust sensing device for closing the valve, and one form of auxiliary control for closing the valve a further amount;

FIG. 2a shows an alternative form of secondary control;

FIG. 3 is a temperature time graph showing the drying cycle when a high initial temperature is employed and is modulated as drying progresses to a predetermined exhaust temperature; a

FIG. 4 is a temperature time graph showing the drying" cycle when a low initial temperature is employed and is modulated as the drying progresses to a predetermined exhaust temperature; and

FIG. 5 is a time temperaturegraph showing the drying cycle according to the practice of the invention in which a high initial temperature is employed followed by a relatively lowtemperature.

Referring to the drawings (FIG. 1), the dryer is like that shown in my pending application Serial No. 97,505, filed March 22, 1961, how Patent No. 3,139,273, comprising a substantially rectangular housing 10 containing, near the top, a rotatably supported, perforated basket 12. A heat distributor 14, situated above the basket, has communication at one end with the upper end of a duct 16,

by means of which hot air is delivered to the distributor and from thence through ports 18 to the basket. A burner unit 20 is mounted below the lower end of the duct 16 for supplying a combustible gas for mixing with air in the duct so that, as it burns, it draws additional air into the duct and forces it upwardly into the distributor and from thence through the basket at a high enough temperature to effect drying. As described in the aforesaid pending application, the rapidly rising hot air induces additional air at the lower end of the duct 16 to be drawn in in sufficient quantity to eifect a complete and etficient combustion of the gas. To augment the natural upflow of the hot gases and to draw the hot gasesthrough the basket 12, an exhaust fan 22 is mounted at the base of the housing 10 adjacent anopening 24 extending rearwardly from the housing 10. Acontrolled flow of heated air is maintained through the basket by the exhaust fan and suitably placed bafiles in and around the basket, as shown in the aforesaid pending application for patent.

Fuel gas is supplied to the buners 20 from a suitable source through a shut-01f cock 26 and conductor 28. A safety valve 30 in the conductor 28 provides for shutting oif the gas in the event of excessive surface temperature at the top of the combustion chamber and to prevent flow of gas in the absence of ignition of the pilot flame. A valve V in the conduit provides for interrupting the flow of gas in response to failure of the exhaust fan, inadequate air flow and excessive exhaust temperature.

As disclosed in my pending application, a modulating valve 32 (FIG. 2) is interposed in the conductor 28. The valve 32 contains a port 34, a valve disc 36 supported by a stem 38 for movement to and from the port, and a motor 40 in the form of a bellows or silphon fixed to one end of the rod. A bulb 44 filled with a liquid or gas which may be at atmospheric or subatmospheric pressure,

connected to the silphon by a capillary tube 42, provides means for effecting expansion and contraction of the silphon to control the flow of gas through the port. The bulb 44 is supported within the housing below the basket so as to be in the path of the moist air exhausted from the basket by the exhaust fan. As the temperature of the exhaust increases, the valve 32 is progressively closed to reduce the input of the burner.

In order to effect rapid drying it is desirable to supply the maximum number of B.t.u. possible While the load contains a large amount of free and absorbed water and to effect modulation with reference to this high level input in proportion to the evaporation of the water. The temperature of the exhaust at this high level input however is too high for safe drying near the end of the cycle when most of the water has been evaporated even though the gas valve controlling the input has been closed to the full extent provided by the sensing bulb 44. As a result, some or all of the load may be damaged by scorching and if not will be left with a harsh bone-dry feel. On the temperature-time graph shown in FIG. 3 the relation of the exhaust temperature to the input temperature is illustrated by the curves X, Y. Although the high level of B.t.u. input represented by the curve Y provides rapid drying, the exhaust temperature represented by the curve X is too high, so that when full modulation is reached as represented by the parallel portion of the curves X, Y, the load is subjected to damagingly high heat and removal of its natural moisture content.

If the input is reduced so that the level of the exhaust is safe for complete drying as indicated by the curves X, Y of FIG. 4, the drying cycle is stretched out so long as to make the operation uneconomical.

The ideal cycle is a combination of the high input illustrated by the curves of FIG. 3 during the initial stages of drying when the load contains a large amount of water both free and absorbed, followed, when the water content has been reduced sufficiently by a low input for the concluding part of the cycle at a temperature which will not damage even the most delicate article contained in the load.

This is attained herein by providing controls, a high level modulated control during which the maximum number of B.t.u. are delivered per unit of time until most of the Water is evaporated followed by a lower level of modulated control during which just enough B.t.u. are supplied to complete the drying cycle and to maintain the load warm and fluffy when it is removed from the dryer.

The high level control is effected by the silphon 40 and bulb 44 described above. The low level control according to this invention is afforded by superimposing on the high level control a secondary control which is brought into operation by the reduction of the moisture content in the load to predetermined level. Since the reducti n in moisture content is proportional to the rise in temperature of the exhaust and this, in turn, controls the temperature of the input, it is evident that the temperature of the input can be employed as a direct measure of the residual moisture and hence to in turn reduce the capacity of the burner. If desired, however, a humidistat may be employed to effect a corresponding control of the burner.

As herein shown in FIG. 2, the valve 32 is moved from its first high capacity position to its second low capacity position by expansion of the valve stem 38 which desirably is comprised of a metal having a relatively high coeflicient of linear expansion. Expansion of the valve stem 38 is effected by a heating coil 45 placed about the stem. A switch 48 connects the heating coil to a source of electric power. A capillary tube 50 and bulb 52 are provided to close a switch 48 at a predetermined temperature. The bulb 52 is placed in the dryer housing adjacent to distributor 18 (FIG. 1) so that it is sensitive to the temperature of the air delivered to the basket. The bulb is provided with a fluid which will expand .at a predetermined temperature to close the switch 48 thereby to supply current to the coil 45. The heating coil by expansion of the stem of the valve disc, moves the disc to the second low capacity position relative to the port independently of the silphon 40, thereby establishing a low level of input that is B.t.u. per unit of time which is consistent with a maximum exhaust temperature which will not damage the load by excessive drying. By placing the bulb 52 close to the distributor, close control of the temperature of the input can be maintained.

Instead of placing a heating coil 46 about the valve stem 38, a coil 46a (FIG. 2a) may be placed about the bulb 44, thereby superimposing the temperature of the coil on the temperature imposed by the exhaust so as to move the valve 36 to its second position through the ex pansion of the silphon rather than the stem. It is evident that in either of the two positions of the valve, modulation continues to take place.

As previously stated a humidistat may be employed to effect this secondary control if desired. If a humidistat were used it would be placed close to the basket so as to be in the path of the moist air leaving the basket.

The compound control is indicated by the curves X Y (FIG. 5). Initially, both the exhaust level and the input level are at a maximum so that a maximum num ber of B.t.u. are supplied to evaporate the water as fast as possible without damage to the load. During this initial period the heat input is modulated in proportion to the removal of water so as not to damage the articles, modulation being effected by the expansion of the silphon in response to the temperature experienced by the bulb 44 in the exhaust stream. During the latter part of the cycle when the residual moisture content reaches a predetermined minimum, the input and exhaust are lowered to a new maximum during which time just enough B.t.u. are supplied to complete drying and maintain the load warm at the end of the cycle.

In each graph the end of the heating cycle is represented by the line tt, and it is evident that by combining the characteristics of the curves in FIGS. 3 and 4, as indicated in FIG. 5, an economically short drying cycle can be obtained with optimum drying of the load.

A direct result of this compound control is to afford means for retaining a controlled moisture content in the articles at the end of the drying cycle instead of bone dryness. The compound control has a further advantage that at the low exhaust level the heat loss during the latter part of the drying cycle is reduced, as indicated by the closely parallel relation of the curves X Y In operation when the instant the dryer is started by de positing a coin of proper denomination, relatively cold air is drawn through the wet load, the bulb 44 is cold and the valve 36 occupies its first position of maximum opening relative to the valve opening 34 for delivering a maximum number of B.t.u. per unit of time. The immediate delivery of high temperature air, however, heats the bulb 52 up to temperature which will energize the coil 46 so as to move the valve 36 to its second position of lower B.t.u. delivery. This condition, however, will exist for only a short time, because the bulb 44 will hold the valve wide open as its second position so that warm air will commence to come through the load, and will close the gas valve at the second position thereby reducing the input so that the temperature at the input will be below that necessary to effect expansion of the fluid in the bulb 52 and hence the switch 48 will be opened. The control Will therefore be transferred back to the bulb 44 and the valve as will be returned to its first position. While the valve remains in its first position it will, of course, be subjected to modulation by the silphon in proportion to the removal of water from the load until the temperature of the input reaches a predetermined maximum, which, as pointed out above, will be indicative of a minimum residual water content, whereupon the bulb 52 will again be heated to a point which will expand the fluid therein and close the switch. Closing the switch heats the coil and this, in turn, moves the valve again to its second position to reduce the capacity of the burner. This condition will continue to the end of the cycle.

By choosing a bulb 52 of the desired sensitivity, the capacity of the burner may be reduced to whatever extent is desired to control the residual moisture and/or prevent excessive drying.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention'includes all modifications and equivalents which fall within the scope of the appended claims.

I claim: v

1. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which the air enters the chamber means and an outlet means through which air is exhausted, variable capacity means having an on condition for supplying heated air to the chamber means and an off condition in which no heat is supplied thereto, means operable to change the capacity of said variable capacity means from a predetermined level of said on condition to a predetermined lower level thereof, means for modulating said variable capacity means at each level of said on condition, and other means operable to effect operation of the variable capacity means when the residual moisture content of the material reaches a predetermined minimum.

2. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which the air enters the chamber means and an outlet means through which the air is exhausted, first means having an on condition for supplying heated air to the chamber means, and an off condition wherein no heat is supplied thereto, second means operable to change the capacity of said first means from a predetermined level of said on condition to a predetermined lower level thereof, third means responsive to the temperature of the exhaust air to modulate said first means relative to each level of said on condition, and fourth means responsive to the temperature of the air supplied to the chamber means to effect operation of said second means.

3. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which air enters the chamber means and an outlet means through which air is exhausted, a burner, for heating the air entering the chamber means, a conductor connecting the burner to a source of gas, a valve situated in the conductor having predetermined first and second open positions of larger and smaller flow capacity for controlling the flow of gas to the burner, means for modulating the valve opening relative to each of the first and second open positions, and other means associated with the valve operative to change the valve opening from said first to said second position when the residual moisture content of the material reaches a predetermined minimum.

4. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a fiow of airthrough the chamber means including an inlet means through which air enters the chamber means and an outlet means through which air is exhausted, a heater adjustable to supply heat to the chamber means at different levels, adjustment means operable to effect adjustment from a predetermined high level to a predetermined lower level, a sensing device responsive to the temperature of the exhaust to modulate the temperature of the air at each level, and another sensing device responsive to the temperature of the air supplied to the chamber means to effect operation of the adjustment means.

5. In a dryer, a drying chamber means for holding a quantity of material to be dried, means forestablishing a flow of air through the chamber means including an in- 6 let means through which air enters the chamber means and an outlet means through which air is exhausted, a heater having an on condition for supplying heat to said chamber and an off condition wherein no heat is supplied thereto, said heater being adjustable to supply heat to the chamber means at different levels of said on condition, means sensitive to the temperature of the exhaust for modulating the heat supplied to each level of said on condition, and means sensitive to the temperature of the input for effecting adjustment of the heater to a lower level, of said on condition.

6. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which air enters the chamber means and an outlet means through which air leaves the cham ber means, a burner for heating the air entering the chamber means, a conductor connecting the burner to a source of gas, a valve in said conductor having first and second positions for controlling the flow of gas to the burner in different amounts, thermal means responsive to the temperature of the input air to shift said valve from the first to the second position, and other means associated with the valve responsive to the temperature of the exhaust air to modulate the valve opening at each of its first and second positions.

7. In a dryer, a drying chamber means for holding a quantity of material'to be dried, means for establishing a flow of air through the chamber means including an inlet means through which the air enters the chamber means and an outlet means through which air leaves, a burner for heating the air entering the chamber means, a con ductor connecting the burner to a source of gas, a valve in said conductor comprising a port and valve disc supported for movement relative thereto by a stern, said valve having first and second positions for controlling the flow of gas to the burner, means associated with the valve stem operating to effect elongation of the valve stem thereby to move the valve disc from said first to said sec ond position, and means connected tothe valve stem for shifting the stem and hence the valve disc bodily relative to the port in either of its first and second positions.

8. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which air enters the chamber means and an outlet means through which air is exhausted, a burner for heating the air entering the chamber means, conductor means for connecting said burner to a source of fuel, a valve in said conductor comprising a port and valve disc supported by a stem for movement relative to the port from a first position of high input to a second position of lower input, a heating coil for effecting linear expansion of the valve stem when the moisture content of the articles reach a predetermined minimum, and a thermal expansion motor connected to the stem and operable to shift the stem axially relative to the port, said thermal expansion motor being responsive to the temperature of the exhaust to effect modulation of the valve disc relative to each position by axial movement of the stem relative to the port.

9. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which air enters the chamber means and an outlet means through which air is exhausted, a burner for heating the air entering the chamber means, conductor means for connecting said burner to a source of fuel, a valve in said conductor comprising a port and valve disc supported by a stem for movement relative to the port, from a first open position of high input to a second open position of lower input by linear movement of the stem, an expansion motor operable to effect movement of the stem and hence the valve, said expansion motor being responsive to a change in temperature to modulate the valve at each of its first and second open positions, and means for superimposing on the motor a temperature of predetermined amount when the residual moisture left in the material reaches a predetermined amount.

10. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which air enters the chamber means and an outlet means through which air leaves the chamber means, a burner for heating the air entering the chamber means, conductor means for connecting said burner to a source of fuel, a valve in said conductor means having predetermined first and second positions, an expansion motor connected to the valve, a bulb connected to the motor for supplying fluid pressure thereto, means supporting said bulb in the path of the exhaust from the chamber means, a heating coil surrounding said bulb operable to impose a predetermined additional amount of heat on the bulb in addition to the heat imposed thereon by the exhaust air, said coil being normally de-energized, and a sensing device sensitive to a predetermined temperature of the input air to energize said coil.

11. In a dryer, a drying chamber means for holding a quantity of material to be dried, means for establishing a flow of air through the chamber means including an inlet means through which air enters the chamber means and an outlet meansthrough which air leaves the chamber means, a burner for heating the air entering the chamber means, conductor means for connecting said burner to a source of fuel, a valve in said conductor having predetermined first and second positions of larger and smaller capacity, an expansion motor connected to said valve, a bulb connected to the motor for supplying pressure fluid thereto, means supporting the bulb in the path of the exhaust from the chamber means, a heating coil surrounding said bulb operable to subject the bulb to a predetermined additional amount of heat, said coil being normally de-energized, a switch operable to energize the coil, and a bulb supported in the path of the input air operably connected to the switch, said bulb being responsive to a temperature of predetermined level in the input to actuate said switch.

References Cited by the Examiner UNITED STATES PATENTS 2,767,923 10/56 Matthews 2369 2,859,025 11/58 StrObeI 26333 3,004,713 10/61 Thorsheim 23668 3,022,987 2/62 Thorsheirn 26333 X 3,123,448 3/64 Fleer 263-33 CHARLES SUKALO, Primary Examiner.

PERCY L. PATRICK, Examiner. 

1. IN A DRYER, A DRYING CHAMBER MEANS FOR HOLDING A QUANTITY OF MATERIAL TO BE DRIED, MEANS FOR ESTABLISHING A FLOW OF AIR THROUGH THE CHAMBER MEANS INCLUDING AN INLET MEANS THROUGH WHICH THE AIR ENTERS THE CHAMBER MEANS AN AN OUTELT MEANS THROUGH WHICH AIR IS EXHAUSTED, VARIABLE CAPACITY MEANS HAVING AN ON CONDITION FOR SUPPLYING HEATED AIR TO THE CHAMBER MEANS AND AN OFF CONDITION IN WHICH NO HEAT IS SUPPLIED THERETO, MEANS OPERABLE TO CHANGE THE CAPACITY OF SAID VARIABLE CAPACITY MEANS FROM A PREDETERMINED LEVEL OF SAID ON CONDITION TO A PREDETERMINED LOWER LEVEL THEREOF, MEANS FOR MODULATING SAID VARIABLE CAPACITY MEANS AT EACH LEVEL OF SAID ON CONDITION, AND OTHER MEANS OPERABLE TO EFFECT OPERATION OF THE VARIABLE CAPACITY MEANS WHEN THE RESIDUAL MOISTURE CONTENT OF THE MATERIAL REACHES A PREDETERMINED MINIMUM. 